Caustic treatment of fuel oils



Nov. 9, 1965 -r. DRESSER CAUSTIC TREATMENT OF FUEL OILS Filed Aug. 20. 1962 E .m& N N% m EF- T. V T m A E M *2 R 0 VJ H j 8a T 3 83 11138 HEILVM United States Patent 3,216,927 CAUSTIC TREATMENT OF FUEL OILS Thorpe Dresser, Markham, BL, assignor to Sinclair Research, Inc., Wilmington, DeL, a corporation of Delaare Filed Aug. 2c, 1952, Ser. No. 217,816 Claims. c1. 2cs 2s4 This invention relates to an improved method in the chemical treatment of cracked distillate fuel oils. More particularly, the present invention relates to the removal of acidic organic material from cracked distillate fuel oils. Specifically the present invention relates to an improved method for the stabilization of cracked distillate fuel oils by the removal of organic acidic substrates, particularly cresylic acid from the oil.

Many petroleum distillate fuel oils of the type used both in domestic and industrial burners deteriorate in storage either with respect to color or sedimentation or both. Several methods of treatment are commonly known to increase the stability of these fuel oils, i.e. acid treating, caustic treating and solvent treating. In the stabilization of such fuel oils by caustic treatment, it is known to treat cracked distillate fuel with concentrated, aqueous solutions of potassium hydroxide or sodium hydroxide in order to improve the stability of the oil. The cracked fuel oils boil primarily in the range of about -450 to 750 F. and contain upwards of about 200 parts per million of phenolic and thio aromatic materials.

In one type of operation of the process, the fuel oil to be treated and the potassium hydroxide or sodium hydroxide solution are intimately contacted, and the mixture is then permitted to settle into three phases, namely, an upper layer of treated oil, a lower layer of potassium hydroxide or sodium hydroxide solution, and a middle layer composed of the alkali metal salts of extracted acidic organic material such as for instance, potassium or sodium cresylates, and potassium hydroxide or sodium hydroxide solution. The middle layer is discarded, and the potassium hydroxide or sodium hydroxide usually after regeneration, is recycled. See for instance Petroleum Refining With Chemicals, Kalichevsky and Kobe, 1956, Elsevier Publishing (30., pages 161-163.

In the operation of the process just described, it is desirable from the standpoint of economy that the middle layer contain as high as possible a concentrate of cresylates since when this is accomplished the amount of potassium hydroxide or sodium hydroxide solution rejected along with the cresylates is minimized. It has been discovered that by using as the treating agent certain solutions which are mixtures of both potassium hydroxide and sodium hydroxide in water the middle layer has a higher concentration of cresylates than if either aqueous potassium hydroxide or aqueous sodium hydroxide were used. This is established by the following table, which shows how the cresylate concentration in the middle layer changes with various weight percentages of potassium hydroxide in the caustic (potassium hydroxide+sodium hydroxide) for various Weight percentages of caustic (potassium hydroxide-l-sodium hydroxide) in the treating solution (potassium hydroxide alone in water, sodium hydroxfi Ice ide alone in water or potassium hydroxide and sodium hydroxide in water, as the case may be).

In the operation of the process of the present invention, the treating solution should contain at least 50% by weight of caustic (potassium hydroxide-l-sodium hydroxide). For instance, when the caustic concentration is 48% by weight, the highest cresylate concentration in the middle layer is obtained with potassium hydroxide in the absence of sodium hydroxide. This is shown by the following table.

TABLE II [48% caustic] Percent KOH in Caustic: Percent Cresylate In the caustic treating of fuel oils using the instant caustic process, low caustic consumption is attained as a result of rejecting the acidic materials in a relatively small phase where they occur as salts of the corresponding acid, for instance, at concentrations from about 25 to 60% and with caustic concentrations from about 20 to 40%, the remainder being essentially water. This process operates in a relatively restricted range of caustic strengths, :limited on the low-caustic side because the desired intermediate cresylate phase will be low in cresylates and may not be in a form that is readily separated from the other phases, and limited on the high caustic side because the caustic containing phases enter a solid or semi-solid state when the caustic approaches about 60% in the caustic-water phase. The weight ratio in the caustic of sodium hydroxide to potassium hydroxide should generally be in the range of about 9:1 to 1:2, preferably the ratio should be from about 7:3 to 1:2 with an especially preferred ratio being about 1:1. Also,

three-component system, caustic-water-cresylic acid at 100%, NaOH, 90% NaOH-l0% KOH, 50% NaOH- 50% KOH and 100% KOH by Weight. The cresylic acid was obtained by acidifying a sodium cresylate mixture obtained by mixing with a 50 B. NaOH solution, a catalytic light cycle oil produced by the fluidized catalytic cracking of a straight run gas oil. The results of tie line experiments based on three component phase studies of the above systems are presented in the tables below.

in the art that while one mixing and settling stage is shown, mixing and settling can take place in a plurality of stages. In settler 14, three phases are formed, the upper phase comprising treated oil; the middle phase comprising acidic organic impurities in the form of alkali salts removed from the oil, chiefly cresylates along with some caustic and water; and the bottom phase comprising caustic and water.

The treated oil flows through line 18 to line and is combined with wash-Water entering by line 24. The treated oil and wash-Water are mixed to dissolve and remove alkali metal hydroxide with which the oil may.

TABLE III [Tie line experiments with NaoH-H o-cresylate system] Wt. Percent of Mixture Conjugate Phase Composition, Wt. Percent NaOH Upper Layer Lower Layer NaOH Cresylate H O H O+Na0H NaOH Cresylate H 0 N aOE H 0 TABLE IV [Tie line experiments with eaustic-lElzo-cresylate system (caustic-10% KOH, KOH, KOH)] Wt. Percent Conjugate Phase Compositions, Wt. Percent NaOH Phases 0 Caustic Remarks Upper Layer Lower Layer res- N aOH KOH ylate H20 Caustic KOH NaOH KOH Cres- H O NaOH KOH H2O +HO ylate 34 4 3. 9 24. 6 37. 1 50. 8 9 31. 5 3. 5 27.8 37. 2 43. 4 4. 8 51. 8 31 7 3. 6 25. 8 38. 9 47. 0 9 39 1 4. 4 31. 7 24. 8 57.5 9 35. 5 4. 0 30.2 30.3 56. 6 9 32. 1 3. 6 35.0 29. 3 48.1 5. 4 47. 5 22. 5 22. 4 30.0 25. 1 64. 1 1 11. 1 11. 1 62. 5 13. 2 30.3 30.3 39.4 19 9 19.8 29. 9 30. 4 56. 6 1 12. 7 12.7 49. 1 25.5 26. 9 26. 9 46. 2 17 3 17. 2 30. 2 35. 3 49. 4 1 16. 5 16. 5 37. 9 29. 1 23. 4 23. 4 53. 2 0 39. 9 30. 2 29.9 57. 2 0 0 32. 4 48. 3 19. 2 O 53.2 46. 8 0 49. 9 30. 1 20.0 71. 4 0 0 39. 5 30. 5 30.0 56. 8 0 0 32. 1 43. 8 24. 1 0 52. 4 47. 6 0 36. 3 27. 4 36. 3 50.0 0 0 31. 1 39. 8 29. 3 0 47. 5 53.5 0 31. 7 30.0 38. 3 45. 3 0 0 0 29. 1 31. 4 39.5 42. 4 0 0 O 46. 9 28. 3 25. 0 65. 2 0 Formed 0 27. 7 54. 4 17. 9 0 57. 5 42. 5

3 phases-cresylate phase, (0 6 0 liquid caustic phase, and solid caustic phase.

*Solid phase composition-this phase contained some entrained cresylates.

In general, treating temperatures in this invention are from about 90 to 170 F., preferably about to F. The ratio of oil to treating solution fed to the treat ing zone is usually about to 94, preferably about to The separation temperatures are similar to the above and in the usual operation treating and separation Will be performed in the same vessel.

The present invention may be better understood by reference to the attached figure which illustrates a preferred embodiment. A cracked distillate fuel oil is pumped from a source not shown through line 2 to water settler 4 Where excess water is removed from the distillate fuel oil. The excess water is taken from the system by line 7. The oil reduced in its water content goes overhead by lines 6 and 8 and is mixed with a caustic solution entering by line 12. The oil and the aqueous metal hydroxide treating solution enter treater-settler 14 via line 16. It will be understood by those skilled 75 from the system or treated to remove the dissolved alkali hydroxide and returned to the system via line 24.

The middle layer in settler 14, comprising alkali metal salts of acidic organic material, caustic and water, is removed via line 34. This solution may be further treated by means not shown for recovery of the acidic material as a by-product through acidification of the salt phase with a mineral acid such as HCl or H 80 The bottom phase, comprising caustic solution (NaOH and KOH) is removed from settler 14, by line 36 and conveyed through pump 38 to line 40 and then to line 42 where this stream may be mixed with a caustic solution, introduced into the system by line 44. The newly introduced solution is of strength such that when the recycled caustic solution is re-introduced into the treater 14 via lines 46 and 12, the overall caustic solution contains 50 and 60 percent by weight of the caustic mixture, i.e. of total sodium hydroxide and potassium hydroxide in their desired weight ratios. Alternatively, instead of adding more caustic to keep the desired caustic concentration in the caustic solution, the bottom layer may be pumped via lines 40, 42 and 48 to reboiler 50 where the recovered caustic solution is subjected to steam under pressure entering by line 52. Water in the form of steam is removed from the reboiler by line 54, and when the caustic solution contains the desired caustic concentration, it is removed from the reboiler by line 56 and pumped to the treater 14 by lines 58 and 12.

The following example will serve to better illustrate the principles of the present invention.

Example After excess water has been removed by settling at a temperature of about 123 F. and under a pressure of about 70 p.s.i.g., 1800 bbl./day of light cycle oil produced by catalytic cracking gas oil and having the following characteristics are combined with a caustic solution having a caustic concentration of 53% and a NaOHKOH weight ratio of 1:1 such that the ratio of oil to treating solution is 25:1. The oil-caustic mixture is allowed to stratify into three phases in a settler where the temperature is maintained at about 125 F. and at a pressure of about 55 p.s.i.g. The upper layer containing the treating oil is removed and water-washed to remove dissolved alkali hydroxide in the treated Oil. The water washing is conducted at a temperature in the range of about 110 to 125 F. and under a pressure of about 30 p.s.i.g. The treated oil is recovered and is analyzed. The phenol and thio-benzene level in the treated oil is 96 p.p.m.

The middle layer is removed and analyzed and shows that it contains 50% alkali metal cresylates, 24% water, 13% NaOH and 13% KOH. This layer was treated with 50% H 50 to a pH of 4.0-6.0 and then separated into two layers. The top layer consisted essentially of cresylic acid. This was removed and stored. The bottom layer was removed and analyzed about 27% by Weight of NaOH, 27% by weight KOH and 46% by weight water. It is recycled and mixed with unstable cracked distillate oil. The overall caustic makeup per day in order to maintain the caustic concentration in the solution between 50 and 60% by weight is 22 gal/day of 50 B. KOH and 19 gaL/day of 50 B. NaOH.

It is claimed:

1. A method for producing a stabilized, cracked distillate fuel oil which comprises treating in the liquid phase an unstable, cracked distillate fuel oil containing acidic organic material with an aqueous solution selected from the group consisting of a solution containing about 50 to by weight of an alkali metal hydroxide mixture consisting essentially of sodium hydroxide and potassium hydroxide in a weight ratio of NaOH to KOH of about 7:3 to 1:2 and a solution containing about 55 to by weight of an alkali metal hydroxide mixture consisting essentially of sodium hydroxide and potassium hydroxide in a weight ratio of NaOH to KOH of about 9:1 to 1:2 to obtain a liquid mixture of treated oil, alkali metal salts of extracted acidic organic material and an aqueous alkali metal hydroxide mixture, stratifying said liquid mixture to obtain an upper layer comprising treated distillate fuel oil, an intermediate layer comprising said alkali metal salts of extracted acidic organic material and a lower liquid layer of aqueous alkali metal hydroxide mixture and separating said layers.

2. The method of claim 1 wherein the intermediate layer comprises about 25 to 60% by weight of the alkali metal salts of cresylic acid.

3. The method of claim 1 wherein the feed contains more than about 500 p.p.m. phenolics and thio aromatics.

4. The method of claim 3 wherein the weight ratio of distillate fuel oil to treating solution is about 30:1 to 19: 1.

5. The method of claim 4 wherein the treatment is conducted at a temperature of from about F. to F.

6. A method for producing a stabilized, cracked distillate fuel oil which comprises treating in the liquid phase an unstable cracked distillate fuel oil containing acidic organic material with an aqueous solution containing 50 to 60 percent by weight of an alkali metal hydroxide mixture consisting essentially of sodium hydroxide and potassium hydroxide in a weight ratio of NaOH and KOH of about 1:1 to obtain a liquid mixture of treated oil, alkali metal salts of extracted acidic organic material and an aqueous alkali metal hydroxide mixture, stratifying said liquid mixture to obtain an upper layer comprising treated distillate fuel oil, an intermediate layer comprising said alkali metal salts of extracted acidic organic material and a lower liquid layer of aqueous alkali metal hydroxide mixture and separating said layers.

7. The method of claim 6 wherein the intermediate layer comprises about 25 to 60% by weight of the alkali metal salts of cresylic acid.

8. The method of claim 6 wherein the feed contains more than about 500 ppm. phenolics and thio aromatics.

9. The method of claim 8 wherein the weight ratio of distillate fuel oil to treating solution is about 30:1 to 19:1.

10. The method of claim 9 wherein the treatment is conducted at a temperature of from about 120 F. to 130 F.

References Cited by the Examiner UNITED STATES PATENTS 2,773,807 12/56 Blatz 208-284 2,795,532 6/57 Honeycutt 208-284 2,850,434 9/58 Brooks et a1. 208-234 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. A METHOD FOR PRODUCING A STABILIZED, CRACKED DISTILLATE FUEL OIL WHICH COMPRISES TREATING IN THE LIQUID PHASE AN UNSTABLE, CRACKED DISTILLATE FUEL OIL CONTAINING ACIDIC ORGANIC MATERIAL WITH AN AQUEOUS SOLUTION SELECTED FROM THE GROUP CONSISTING OF A SOLUTION CONTAINING ABOUT 50 TO 55% BY WEIGHT OF AN ALKALI METAL HYDROXIDE MIXTURE CONSISTING ESSENTIALLY OF SODIUM HYDROXIDE AND POTASSIUM HYDROXIDE IN A WEIGHT RATIO OF NAOH TO KOH OF ABOUT 7:3 TO 1:2 AND A SOLUTION CONTAINING ABOUT 55 TO 60% BY WEIGHT OF AN ALKALI METAL HYDROXIDE MIXTURE CONSISTING ESSENTIALLY OF SODIUM HYDROXIDE AND POTASSIUM HYDROXIDE IN A WEIGHT RATIO OF NAOH TO KOH OF ABOUT 9:1 TO 1:2 TO OBTAIN A LIQUID MIXTURE OF TREATED OIL, ALKALI METAL 